An agricultural baler is a trailed machine (PTM—pulled type machine) which ensures that agricultural material such as hay, straw, silage or similar crop material that previously has been cut, windrowed or swathed, is picked up from the field by a pick-up unit, fed into a duct and loaded into an elongated baling chamber where it is gathered into bales. A plunger which reciprocates in the front portion of the baling chamber compresses the newly introduced material against the previously introduced material into a parallelepipedic package, and at the same time, gradually advances the package towards the outlet of the baling chamber. As the package reaches a predetermined length as determined by a metering device, a knotter device may be actuated to wrap cord, twine or other flexible binding material around the package and to secure the ends of the binding material together to form a stable bale.
FIG. 1 shows an agricultural baler 10 comprising a main frame 11 which is equipped with a forwardly extending tongue 12 provided at its front end with hitch means (not shown) for coupling the baler 10 to a towing tractor. A pick-up assembly 13 lifts windrowed crop material off the field as the baler 10 is travelled thereover and delivers such material into the front end of a rearwardly and upwardly curved, charge-forming feeder duct 14. The duct 14 communicates at its upper end with an overhead, fore-and-aft extending baling chamber 15 into which crop charges are loaded by a cyclically operating stuffer mechanism 16. A continuously operating packer mechanism 17 at the lower front end of the feeder duct 14 continuously feeds and packs material into the duct 14 as to cause charges of the crop material to take on and assume the internal configuration of the duct 14 prior to periodic engagement by the stuffer 16 and insertion up into the baling chamber 15. The feeder duct 14 may be equipped with means (not illustrated) for establishing whether a complete charge has been formed therein and operating the stuffer mechanism 16 in response thereto. Each action of the stuffer mechanism 16 introduces a “charge” or “flake” of crop material from the duct 14 into the chamber 15.
A plunger 18 reciprocates in a fore-and-aft direction within the baling chamber 15 under action of a pair of connecting or pitman rods 19 which are linked to the crank arms 20 of a gearbox 21 driven by a transmission shaft 22 which is connected to the PTO shaft of the tractor pulling the agricultural baler 10. The reciprocating plunger 18 pushes each new charge introduced into the baling chamber 15 rearwardly and forms the subsequent charges into a parallelepiped package of crop material, which is forced by the same action of the plunger 18 toward a rearmost discharge aperture 23 of the chamber 15.
The gearbox 21 is affixed at its lower section by a set of bolts 26 to the main frame 11.
Theoretically, the gearbox 21 is positioned in the middle of the carrying beam 30, and the baling chamber 15 is placed in line with the carrying beam, such that the plunger 18 is placed in line with the gearbox 21. However, some aberrations within tolerance limits can occur when constructing the main frame 11, which may be done most often for example by welding. As a result the gearbox 21 for driving the plunger 18 and the plunger 18 itself might not be completely aligned. Since high forces of the plunger 18 are demanded by the market (currently up to 230 kN and probably this will rise in the future) a non-perfect alignment of plunger 18 and main frame 11 might result in abnormally fast wearing or even in fractures of parts of the baler 10.
One way to overcome the aberrations of the frame 11 is to guide the plunger 18 by rails, for example a set of bottom and top plunger rails 41, 42 at each side of the plunger 18. A typically used method to mount these rails is to align one rail or one set of rails with a side wall of the baling chamber 15 and to mount the other rail or set of rails parallel thereto at a desired distance, determined by a width dimension of the plunger 18. However, if the frame 11 is distorted, the plunger 18 will not be guided in line with the gearbox 21 and wearing will still happen.